1. Field of the Invention
The present invention relates to an optical receptacle that optically couples a semiconductor optical device installed in an optical transmitting module, an optical receiving module and an optical communication module with an optical ferrule secured in a tip of an optical fiber.
2. Related Prior Art
There are two types in the optical module, independent of the optical transmitting module that installs a light-emitting device and the optical receiving module that installs a light-receiving device, depending on the optical coupling with the optical fiber. That is, one type is that the optical fiber permanently couples with the semiconductor device and the other is that the fiber releasably couples with the semiconductor device through an optical receptacle including a sleeve. The latter type is often called as a receptacle type module, which includes a package that installs a semiconductor optical device, a lens holder, a sleeve that mates with an optical ferrule attached in a tip of the optical fiber, and a housing.
Conventional receptacle is generally made of metal and has a cylindrical shape. As the transmission speed of the optical communication grows higher, recently the speed reaches and exceeds 1 GHz, various subjects have been raised. For the optical transmission module, the driving signal for the laser diode becomes a source of the EMI noise to influence the peripheral electric apparatus and devices. The metal receptacle, in particular, a top portion of the receptacle functions as an antenna to radiate the driving signal as the EMI noise. For the receiving module, the top of the metal receptacle receives the noise radiation from the peripheral, which degrades the quality of the electrical signal converted from the faint receiving optical signal.
Accordingly, it is requested to electrically isolate the top of the receptacle from the metal package that installs the semiconductor device or from the circuit connected to the semiconductor device.
Japanese Patent Application published as JP-2005-070499A has disclosed an optical receptacle that uses an insulating material to enhance the noise reduction performance. FIG. 1 is a schematic drawing of the receptacle shown in this prior document. The rigid sleeve 42, made of ceramics, is press-fitted into the metal holder 43, while, the sleeve 42 receives in a rear portion thereof the metal stopper 45 by press-fitting. Behind the holder 43 is welded with the package of the optical device of the transmitting module or the receiving module.
The sleeve 42 also provides a flange 44 in the outer surface thereof. That is, the sleeve 42 is press-fitted into the flange 44. The holder 43 and the flange, both made of metal, are separated to each other. The sleeve 42 releasably receives the ferrule 47 in the aperture of the front end thereof.
Inserting the ferrule 47 that secures the optical fiber 46 in a center thereof into the sleeve 42, the tip of the ferrule 47 abuts against the stopper 45. Practically, the ferrule generally provides a metal shell that secures the ferrule 47, and this metal shell comes in contact with the flange 44 at the same time of abutting ferrule 47 against the stopper 45. In such configuration, because the sleeve is made of insulating material and the metal holder 43 is physically separated from the metal flange 44, the ferrule 47 may be electrically isolated from the package of the optical module.
However, the arrangement of the receptacle shown in the prior document, the metal stopper 45 is press-fitted into the ceramic sleeve 42 and this ceramic sleeve 42 is press-fitted into the holder 43 at the same portion of the sleeve 42. That is, the sleeve 42 is puts between the metal holder 43 and the metal stopper 45 at the same portion thereof. Further, the metal flange 44 positions in the immediate of the metal holder 43.
It is quite hard to press-fit a member into the second member and to press-fit the second member into the third member at the same portion because the inside member is shrunk as well as the outside member is expanded by the press-fitting. Accordingly, since the second member put between the first and third members is shrunk by the first press-fitting, the second press-fitting of the third member into the second member is necessary to be carried out for the shrunk second member. In the practical receptacle, the second member corresponds to the ceramic sleeve. Therefore, it is often encountered that the ceramic sleeve, made of brittle material, is cracked at the first or second press-fitting without precise control of the physical dimensions of the sleeve itself and the metal stopper 45.